The fight revolves around a security standard called FISMA, which is required for some government contracts.

Google has advertised that its set of online services for government agencies, Google Apps for Government, is FISMA certified. Microsoft's competing product, BPOS-Federal, is not.

But Microsoft found a court filing saying: "On December 16, 2010, counsel for the Government learned that, notwithstanding Google's representations to the public at large, its counsel, the GAO, and this Court, it appears that Google's Google Apps for Government does not have FISMA certification."

Google responded by explaining that the General Services Administration (GSA) certified a slightly different product called Google Apps Premier. The product in question, Google Apps for Government, is basically the same, but has a different name and a couple of new features.

In consulting with GSA last year, it was determined that the name change and enhancements could be incorporated into our existing FISMA certification. In other words, Google Apps for Government would not require a separate application.

FISMA anticipates that systems will change over time and provides for regular reauthorization—or re-certification—of systems. We regularly inform GSA of changes to our system and update our security documentation accordingly. The system remains authorized while the changes are evaluated by the GSA. We submitted updates earlier this year that included, among other changes, a description of the Google Apps for Government enhancements.

So Microsoft did more than take a technicality and blow it way out of proportion. According to Google, Microsoft lied when it called Google a liar.

Why is all this important?

Because earlier this year, Google sued another branch of the government -- the Department of the Interior -- for picking Microsoft's (uncertified) product, saying that it didn't give Google Apps a fair shake. A judge agreed in January, and slapped a restraining order on the DOI.

Microsoft has a lot of valuable software contracts with the government. This incident shows just how seriously Microsoft takes those contracts -- and the kind of tactics it will use to defend them.